TWI865628B - Coating agent for paper, coated paper using same and method for manufacturing coated paper - Google Patents

Abstract

A coating agent for paper, which contains an ethylene-vinyl alcohol copolymer having an ethylene unit content of more than 1 mol% and less than 20 mol%, and a block character of ethylene units of 0.90 to 0.99. Also, a coated paper having such a coating agent coated on paper. The coating agent of the present invention has excellent viscosity stability, and the obtained coated paper has excellent barrier properties and water resistance.

Description

Paper coating agent, coated paper using the same, and method for producing coated paper

The present invention relates to a coating agent for paper containing ethylene-vinyl alcohol copolymer. In addition, the present invention relates to coated paper using the coating agent and a method for manufacturing the same.

Vinyl alcohol polymers, represented by polyvinyl alcohol (hereinafter referred to as "PVA"), are known as water-soluble synthetic polymers and are widely used in raw materials for synthetic fiber vinyl, paper processing agents, fiber processing agents, adhesives, stabilizers for emulsion polymerization and suspension polymerization, inorganic binders, films, etc. In particular, it is known that by coating PVA on paper, the paper strength can be enhanced, and water resistance, oil resistance, gas barrier properties, etc. can be given. Coated paper formed by coating vinyl alcohol polymers on paper is widely used. In addition, vinyl alcohol polymers are also used as auxiliary agents used together with inorganic binders or dispersion stabilizers, etc., which are additives for imparting functionality to paper.

In coated paper, especially in release paper, PVA polymers are generally used as gap filling layers (barrier layers) in order to reduce the gaps between pulp fibers that make up the paper and improve the yield of the polysilicone coated on the paper surface. Among them, partially saponified PVA is preferred due to its excellent barrier properties.

However, partially saponified PVA has poor water resistance. Therefore, during adhesion processing, the PVA may dissolve due to humidification, causing adhesion, or the water-dispersible varnish cannot be used in post-processing. These problems require solutions.

Patent document 1 states that by using a coating liquid containing ethylene-modified PVA and carboxymethyl cellulose, both barrier properties and water resistance can be achieved.

However, the coating liquid has insufficient viscosity stability. In addition, a large number of fibrous precipitates are generated due to shear stress applied to the coating liquid during preparation and coating, and there is room for improvement in process passability. [Prior technical literature] [Patent literature]

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-21788

[Problems to be solved by the invention]

The present invention is completed based on the above situation, and its purpose is to provide a coating agent that has excellent viscosity stability and can obtain a coating paper with excellent barrier properties and water resistance. [Means for solving the problem]

The above-mentioned problem is solved by providing a paper coating agent, which contains an ethylene-vinyl alcohol copolymer having an ethylene unit content of 1 mol % or more and less than 20 mol % and a block character of the ethylene unit of 0.90 to 0.99.

At this time, the coating agent preferably further contains 0.000001 to 0.01 parts by mass of a compound having a molecular weight of 1000 or less and having a conjugated double bond relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer. The saponification degree of the ethylene-vinyl alcohol copolymer is also preferably 80 to 99.7 mol%. The viscosity average polymerization degree of the ethylene-vinyl alcohol copolymer is also preferably 300 to 5000. The coating agent also preferably further contains an ionic polymer.

The above-mentioned problem is also solved by providing a paper coating agent, which contains an ethylene-vinyl alcohol copolymer and an ionic polymer having an ethylene unit content of 1 mol % or more and less than 20 mol %.

At this time, the coating agent preferably further contains 0.000001 to 0.01 parts by mass of a compound having a molecular weight of 1000 or less and having a conjugated double bond relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer. The saponification degree of the ethylene-vinyl alcohol copolymer is also preferably 80 to 99.7 mol%. The viscosity average polymerization degree of the ethylene-vinyl alcohol copolymer is also preferably 300 to 5000.

Coated paper coated with the aforementioned coating agent is a suitable embodiment of the present invention. The aforementioned coated paper is preferably a release paper base paper. The aforementioned coated paper is also preferably an oil-resistant paper. A method for manufacturing coated paper in which the aforementioned coating agent is applied to paper is also a suitable embodiment of the present invention. [Effect of the invention]

The paper coating agent of the present invention containing the aforementioned ethylene-vinyl alcohol copolymer having a specific structure is excellent in viscosity stability. In addition, by using the aforementioned coating agent, a coated paper having excellent barrier properties and water resistance, especially release paper and oil-resistant paper, can be provided.

[Form used to implement the invention]

The paper coating agent of the present invention contains an ethylene-vinyl alcohol copolymer having a ethylene unit content of 1 mol % or more and less than 20 mol % and a block characteristic value of the ethylene unit of 0.90 to 0.99.

[Ethylene-vinyl alcohol copolymer] The characteristics of the ethylene-vinyl alcohol copolymer contained in the paper coating agent of the present invention are: the content of ethylene units is greater than 1 mol% and less than 20 mol%, and the block characteristic value of the ethylene units is 0.90 to 0.99. This part is explained below.

(Block characteristic value of ethylene unit) The block characteristic value of ethylene unit is 0.90 to 0.99, which is a major characteristic of the aforementioned ethylene-vinyl alcohol copolymer. Since the aforementioned block characteristic value is 0.90 or more, the viscosity stability of the coating agent is improved, and at the same time, the barrier property of the obtained coating paper is improved. The block characteristic value is preferably 0.93 or more, and more preferably 0.95 or more. On the other hand, the aforementioned block characteristic value is 0.99 or less. Since the aforementioned block characteristic value is 0.99 or less, the water resistance of the obtained coating paper is improved.

Furthermore, the so-called block characteristic value is a numerical value indicating the distribution of ethylene units and vinyl alcohol units generated by saponification of vinyl ester units, and takes a value between 0 and 2. 0 means that ethylene units or vinyl alcohol units are completely distributed in blocks, and the alternation increases as the value increases, 1 means that ethylene units and vinyl alcohol units exist completely randomly, and 2 means that ethylene units and vinyl alcohol units exist completely alternately. The above-mentioned block characteristic value is obtained by ¹³ C-NMR as follows. First, after saponification of ethylene-vinyl alcohol copolymer to a saponification degree of 99.9 mol% or more, it is fully washed with methanol and dried under reduced pressure at 90°C for 2 days. After dissolving the obtained completely saponified ethylene-vinyl alcohol copolymer in DMSO-d ₆ , the obtained sample is measured at 80°C using 500 MHz ¹³ C-NMR (JEOL GX-500). From the obtained spectrum, the molar fraction of vinyl alcohol-ethylene 2-unit chain (AE), the molar fraction of vinyl alcohol unit (A), and the molar fraction of ethylene unit (E) were calculated by the method described in T. Moritani and H. Iwasaki, 11, 1251-1259, Macromolecules (1978), and the block characteristic value (η) of ethylene unit was calculated by the following formula. η=(AE)/{2×(A)×(E)}

The ethylene-vinyl alcohol copolymer having the block characteristic value of the ethylene unit specified above can be obtained by a special production method including a polymerization step and a saponification step described later. The inventors of the present invention have made intensive research and found that by adopting such a production method, the block characteristic value of the ethylene unit can be successfully controlled. Moreover, it is found that by making the block characteristic value of the ethylene unit within the above range, the viscosity stability of the coating agent is improved, and the barrier properties and water resistance of the obtained coating paper are also improved. The following is a more detailed description of the ethylene-vinyl alcohol copolymer of the present invention.

(Vinyl ester) The ethylene-vinyl alcohol copolymer of the present invention is obtained by copolymerizing ethylene and vinyl ester to obtain an ethylene-vinyl ester copolymer, and then saponifying the ethylene-vinyl ester copolymer. As the vinyl ester used, there can be cited vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, trimethylacetate and vinyl neodecanoate, among which vinyl acetate is preferred.

(Content of ethylene units) The content of ethylene units in the ethylene-vinyl alcohol copolymer of the present invention is 1 mol% or more and less than 20 mol%. When the content of ethylene units is less than 1 mol%, the water resistance of the obtained coated paper is reduced. The content of ethylene units is preferably 1.5 mol% or more, more preferably 2 mol% or more, and particularly preferably 2.5 mol% or more. On the other hand, when the content of ethylene units is 20 mol% or more, the ethylene-vinyl alcohol copolymer becomes insoluble in water, and the preparation of an aqueous solution becomes difficult. The content of ethylene units is preferably 15 mol% or less, more preferably 10 mol% or less, and particularly preferably 8.5 mol% or less.

The content of ethylene units can be determined, for example, from ^{the 1} H-NMR of ethylene-vinyl ester copolymers which are precursors or reacetylated products of ethylene-vinyl alcohol copolymers by the following method. After reprecipitation and purification of the sample ethylene-vinyl ester copolymer three or more times using a mixed solution of n-hexane and acetone, the ethylene-vinyl ester copolymer is dried under reduced pressure at 80°C for 3 days to prepare an ethylene-vinyl ester copolymer for analysis. The obtained ethylene-vinyl ester copolymer is dissolved in DMSO-d ₆ and measured by ¹ H-NMR (500 MHz) at 80°C. The content of ethylene units can be calculated using the peak of the main chain methylene group derived from vinyl ester (4.7 to 5.2 ppm) and the peak of the main chain methylene group derived from ethylene and vinyl ester (0.8 to 1.6 ppm).

(Saponification degree) The saponification degree of the ethylene-vinyl alcohol copolymer of the present invention is preferably 80 mol% or more, more preferably 85 mol% or more, and particularly preferably 90 mol% or more. On the other hand, the saponification degree is preferably 99.7 mol% or less, and more preferably 99 mol% or less. When the saponification degree is above the above lower limit, the water resistance of the obtained coated paper is further improved. On the other hand, when the saponification degree is below the above upper limit, the barrier property of the obtained coated paper is further improved, and the aforementioned ethylene-vinyl alcohol copolymer can be easily and stably produced. The saponification degree of the aforementioned ethylene-vinyl alcohol copolymer can be measured in accordance with JIS K6726 (1994).

(Viscosity average degree of polymerization) The viscosity average degree of polymerization of the ethylene-vinyl alcohol copolymer of the present invention is preferably 300 or more, more preferably 500 or more, particularly preferably 700 or more, and particularly preferably 900 or more. On the other hand, the viscosity average degree of polymerization is preferably 5000 or less, more preferably 4000 or less, particularly preferably 3500 or less, and particularly preferably 2400 or less. When the viscosity average degree of polymerization is above the above lower limit, the water resistance of the resulting coated paper is further improved. On the other hand, when the viscosity average degree of polymerization is below the above upper limit, the coating solution (preferably an aqueous solution) in which the ethylene-vinyl alcohol copolymer has been dissolved has an appropriate viscosity and is therefore easy to handle. The viscosity average degree of polymerization P can be measured in accordance with JIS K6726 (1994). That is, the ethylene-vinyl alcohol copolymer of the present invention can be purified by re-saponifying to a saponification degree of 99.5 mol% or more, and then the limiting viscosity [η] (L/g) measured in water at 30°C can be obtained by the following formula: P = ([η] × 10000/8.29) ^(1/0.62)

(Other monomer units) The ethylene-vinyl alcohol copolymer of the present invention may contain other monomer units other than vinyl alcohol units, ethylene units and vinyl ester units as long as the effects of the present invention are not impaired. As such other monomer units, there can be mentioned α-olefins derived from propylene, n-butene, isobutylene, etc.; acrylic acid and its salts; acrylic acid esters; methacrylic acid and its salts; methacrylic acid esters; acrylamide; N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidepropyldimethylamine and its salts or its quaternary salts, N-hydroxymethylacrylamide and its derivatives, and acrylamide derivatives; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or its quaternary salts, N- Methacrylamide derivatives such as hydroxymethyl methacrylamide and its derivatives; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; halogen vinyls such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid, fumaric acid and their salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane; units of isopropylene acetate, etc. The content of these other monomer units varies depending on the purpose of use or application, but is preferably less than 10 mol %, more preferably less than 5 mol %, even more preferably less than 1 mol %, and particularly preferably less than 0.5 mol %.

[Method for producing ethylene-vinyl alcohol copolymer] A suitable method for producing ethylene-vinyl alcohol copolymer of the present invention is a method for producing ethylene-vinyl alcohol copolymer comprising: reacting ethylene with vinyl ester to obtain ethylene-vinyl ester copolymer, and then saponifying the ethylene-vinyl ester copolymer, wherein the method comprises the step of (a) contacting a solution containing vinyl ester with a gas containing ethylene while stirring the solution in a polymerization tank using a wide blade so that the stirring power Pv per unit volume becomes 0.5 to 10 kW/ ^m3 and the Froude number Fr becomes 0.05 to 0.2. By contacting the solution containing vinyl ester with the gas containing ethylene in this way, the block characteristic value of the ethylene unit of the ethylene-vinyl alcohol copolymer can be made into the above range. The above-mentioned manufacturing method is described in detail below.

(Polymerization step) In the polymerization step, ethylene-vinyl ester copolymer is obtained by reacting (copolymerizing) ethylene and vinyl ester. As a method for copolymerizing ethylene and vinyl ester, a solution polymerization method of polymerizing ethylene and vinyl ester in an organic solvent such as alcohol is preferred. As the above-mentioned alcohol, lower alcohols such as methanol and ethanol can be mentioned, and methanol is particularly preferred. As the initiator used for the polymerization, well-known initiators such as azo-based initiators or peroxide-based initiators such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate can be mentioned.

In the polymerization step, a chain transfer agent may be allowed to coexist for the purpose of adjusting the viscosity average polymerization degree of the obtained ethylene-vinyl ester copolymer. Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol; thiocarboxylic acids such as thioacetic acid; halogenated hydrocarbons such as trichloroethylene and perchloroethylene. Among them, aldehydes and ketones are preferably used. The amount of the chain transfer agent added is determined according to the chain transfer constant of the chain transfer agent added and the viscosity average polymerization degree of the desired ethylene-vinyl ester copolymer, but is usually 0.1 to 10 parts by mass relative to 100 parts by mass of the vinyl ester used.

In the polymerization operation, any polymerization method of continuous method, semi-batch method and batch method can be adopted, but continuous method is preferred. As the polymerization reactor, there can be cited continuous tank reactor, batch reactor, tube reactor, etc., but continuous tank reactor is preferred.

The specific polymerization apparatus and the polymerization steps using the same are described below with reference to the drawings. FIG1 is a schematic diagram of the polymerization apparatus used in Example 1. The apparatus is a continuous tank reactor, and the polymerization tank 1 is connected to the heat exchanger 2 through pipes 3 and 4. In the heat exchanger 2, vinyl ester and ethylene can be in countercurrent contact.

A plurality of conduits 5, 6, and 7 are connected to the polymerization tank 1. The number or arrangement of the conduits is not limited to the form shown in the figure. Ethylene, polymerization initiators, and organic solvents are supplied to the polymerization tank 1 through these conduits. The ratio of the raw materials introduced into the polymerization tank per unit time is preferably 0.1 to 20 parts by mass of ethylene, 1 to 100 parts by mass of organic solvent, and 0.00001 to 1 part by mass of polymerization initiators relative to 100 parts by mass of vinyl ester. Depending on the circumstances, vinyl ester or other monomers may also be supplied through these conduits. The reaction liquid in the polymerization tank 1 is continuously discharged from the reaction liquid outlet pipe 9 connected to the bottom of the polymerization tank 1.

A stirrer 8 having a wide blade as a stirring blade is installed in the polymerization tank 1. By using the wide blade, the solution containing the vinyl ester is stirred while being contacted with a gas containing ethylene, so that ethylene and the vinyl ester react to obtain an ethylene-vinyl ester copolymer.

As a stirring blade for stirring the solution containing ethylene ester, it is preferable to use a wide paddle. FIG2 is a schematic diagram showing an example of a wide paddle used in the present invention. As shown in FIG2, a wide paddle having a width b is a characteristic of the wide paddle. The width b of the wide paddle can be appropriately adjusted according to the capacity of the polymerization tank 1, etc., but as described later, it is preferably 1 to 10 m. By using such a paddle, the solution can be mixed evenly from the bottom to the liquid surface, and at the same time, the solution containing ethylene ester can absorb ethylene more efficiently. The aforementioned wide paddle may be a single-stage (e.g., a Maxblend blade) or a multi-stage (e.g., a Fullzone blade). From the viewpoint of making the vinyl ester absorb ethylene more efficiently, the liquid level of the solution is preferably near the upper end of the stirring blade during the stirring of the solution containing the vinyl ester. As wide blades, specifically, there can be cited the Maxblend blade (Sumitomo Heavy Industries, Ltd.), the Fullzone blade (Kobelco Environmental Solutions Co., Ltd.), the Sanmeler blade (Mitsubishi Heavy Industries, Ltd.), the Hi-Fi Mixer blade (Soken Chemical Co., Ltd.), the Super-Mix blade (Satatake Chemical Industries, Ltd., Super-Mix MR203, Super-Mix MR205), the Bendleaf blade (Hakko Industrial Co., Ltd.), etc.

The ethylene pressure in the polymerization tank during polymerization is preferably 0.01 to 0.9 MPa, more preferably 0.05 to 0.8 MPa, and particularly preferably 0.1 to 0.7 MPa. The polymerization rate of the vinyl ester at the outlet of the polymerization tank is not particularly limited, but is usually preferably 10 to 90%, more preferably 15 to 85%.

The polymerization temperature is not particularly limited, but is usually preferably 0 to 180°C, more preferably 20 to 160°C, and particularly preferably 30 to 150°C.

When reacting ethylene with vinyl ester, the solution is preferably stirred in a polymerization tank in such a manner that the stirring power Pv per unit volume of the solution containing the vinyl ester becomes 0.5 to 10 kW/m ^3. When the stirring power is less than 0.5 kW/m ³ , the amount of ethylene absorbed by the vinyl ester becomes insufficient, and the uniformity of the reaction solution also becomes insufficient, and an ethylene-vinyl alcohol copolymer having a block characteristic value of the ethylene unit within the above range cannot be obtained. The stirring power is more preferably 1 kW/m ³ or more, and more preferably 1.5 kW/m ³ or more. On the other hand, when the stirring power exceeds 10 kW/m ³ , the power used for operation becomes very large, which is not suitable for industry. The stirring power is more preferably 7 kW/m ³ or less, and more preferably 5 kW/m ³ or less. The stirring power Pv per unit volume of the solution containing vinyl ester can be measured by the method described in the examples described later.

The Fr is the ratio of the inertial force to the gravity, which is defined by the following formula and is an indicator of the shape of the vortex on the liquid surface. Fr = n ² × d/g n: number of revolutions of the agitator blade (rps) d: diameter of the agitator blade (m) g: acceleration due to gravity (m/s ² )

When reacting ethylene with vinyl ester, the solution containing vinyl ester is preferably stirred in a polymerization tank in such a manner that the Fluor number Fr becomes 0.05 to 0.2. By adjusting the Fluor number Fr to the above range and controlling the shape of the vortex on the liquid surface, it is believed that since ethylene is appropriately absorbed in the vinyl ester, an ethylene-vinyl alcohol copolymer having a block characteristic value of ethylene units within the above range can be easily obtained. The Fluor number Fr is more preferably not less than 0.06, and particularly preferably not less than 0.07. On the other hand, the Fluor number Fr is more preferably not more than 0.18, and particularly preferably not more than 0.15. In order to make the Fluor number Fr within the above range, it is sufficient to appropriately change the number of rotations n of the stirring blade or the diameter d of the stirring blade.

The stirring blade diameter d of the wide blade can be adjusted so that the stirring power Pv and the Förster number Fr are within the above ranges. There is no particular limitation, but from the viewpoint of improving the ethylene absorption efficiency, it is preferably 0.5 to 5 m. The stirring blade diameter d is more preferably 0.75 m or more. On the other hand, the stirring blade diameter d is more preferably 4 m or less. The stirring blade diameter d is the value obtained by doubling the distance from the rotation axis to the front end of the blade (the point farthest from the rotation axis).

The width b (length in the height direction) of the paddle blade can be adjusted according to the capacity of the polymerization tank 1, etc., and is not particularly limited. However, from the viewpoint of improving the ethylene absorption efficiency, the width b is preferably 1 to 10 m. The width b is more preferably 1.5 m or more. On the other hand, the width b is more preferably 8 m or less.

The ratio (b/d) of the width of the paddle (blade width) b to the diameter of the agitator blade d may be determined according to the shape of the polymerization tank 1, etc., and is not particularly limited, but is preferably 1 or more from the viewpoint of improving the ethylene absorption efficiency. On the other hand, the ratio (b/d) is usually 2.5 or less.

The shape of the polymerization tank 1 is not particularly limited, but generally a substantially cylindrical one is used. At this time, the wide paddle is arranged in the substantially cylindrical polymerization tank 1 in such a manner that the rotation axis of the polymerization tank 1 and the rotation axis of the wide paddle are aligned. The ratio (d/D) of the diameter d(m) of the stirring blade to the inner diameter D(m) of the polymerization tank is not particularly limited as long as it does not hinder the effect of the present invention, and can be appropriately adjusted according to the polymerization tank used, but is generally 0.4 to 0.9. The capacity of the polymerization tank is not particularly limited, but is generally 1 to 200 kl.

The number of revolutions n of the stirring blade can be adjusted in such a way that the stirring power Pv and the Fr are within the above ranges. There is no particular limitation, but it is preferably 0.5 to 1.35 rps. When the number of revolutions n is less than 0.5 rps, since the overcooling of the polymerization solution near the heat transfer surface becomes easy, a gel-like substance is generated on the inner wall of the polymerization tank, and long-term operation may become difficult. On the other hand, when the number of revolutions n exceeds 1.35 rps, when a polymerization solution with low viscosity is used, the solution may jump and adhere to the inner wall of the gas phase of the polymerization tank. If such an adhered substance solidifies and mixes into the polymerization solution, it will form a foreign matter, and stable operation may be impossible.

In the past, when manufacturing ethylene-vinyl alcohol copolymers, the stirring power per unit volume, which is an index of stirring intensity, was controlled. However, the stirring power is affected by various factors such as the volume, viscosity and density of the reaction solution, the shape of the polymerization tank, and the shape and rotation number of the stirring blade. Therefore, it is difficult to highly control the blockiness of the ethylene unit by controlling only the stirring power, resulting in the elongation of the ethylene chain (blocking of the ethylene unit), and the block characteristic value of the ethylene unit in the obtained ethylene-vinyl alcohol copolymer is less than 0.90. In addition, due to the elongation of the ethylene chain, the hydrophobic interaction between molecules becomes stronger, and the barrier property of the obtained coating paper cannot be said to be sufficient. Furthermore, when carboxymethyl cellulose is added to ethylene-vinyl alcohol copolymer, the barrier properties are improved but the viscosity stability of the aqueous solution is also reduced. The inventors have devoted themselves to studying this problem and found that by carrying out the polymerization reaction under specific conditions, a copolymer with a shorter ethylene chain (the position of the ethylene unit is random) can be obtained, which successfully improves the viscosity stability of the aqueous solution of ethylene-vinyl alcohol copolymer and the barrier properties of the resulting coating paper at the same time.

From the viewpoint of more highly controlling the block characteristic value of the ethylene unit, in the aforementioned production method, the aforementioned polymerization tank used in the polymerization step is connected to a heat exchanger through a pipe, and when the ethylene-vinyl ester copolymer is obtained, it is preferred to further include: (b) a step of introducing the ethylene-containing gas existing in the gas phase portion of the aforementioned polymerization tank into the aforementioned heat exchanger, (c) a step of supplying vinyl ester to the aforementioned heat exchanger, (d) a step of bringing the vinyl ester into contact with the ethylene-containing gas in the aforementioned heat exchanger, and (e) a step of withdrawing the vinyl ester in which ethylene has been dissolved from the aforementioned heat exchanger and introducing it into the aforementioned polymerization tank. The vinyl ester may be directly supplied to the polymerization tank without passing through a heat exchanger. However, in such a case, the vinyl ester is allowed to absorb ethylene in advance in a heat exchanger before being supplied to the polymerization tank. Since ethylene is efficiently absorbed by the vinyl ester, the block characteristic value of the ethylene unit is highly controlled. A part of the vinyl ester supplied to the polymerization tank may be brought into contact with a gas containing ethylene in a heat exchanger. However, it is preferred that the entirety of the vinyl ester supplied be brought into contact with a gas containing ethylene in a heat exchanger.

The heat exchanger used is not particularly limited. From the viewpoint of efficient absorption of ethylene, a heat exchanger with a large surface area is preferred. For example, there can be cited a vertical wet wall heat exchanger, a vertical wet wall multi-tube heat exchanger, a heat exchanger provided with a jacket and/or a coil in a packed tower, a porous plate or a bubble-cap absorber, etc. Among them, a vertical wet wall multi-tube heat exchanger is preferred.

In the apparatus shown in FIG1 , a vertical wet wall multi-tube heat exchanger is used as the heat exchanger 2. A vinyl ester introduction pipe 10 is connected to the heat exchanger 2, and vinyl ester is supplied to the upper part of the heat exchanger 2 through the pipe. As the raw material, vinyl ester can be used alone or in the form of a mixed solution containing the organic solvent and vinyl ester, but the latter is preferred.

The heat exchanger 2 shown in FIG1 is connected to refrigerant pipes 11 and 12. The position of the pipes is not limited to the form shown in the figure. It is preferred that the refrigerant is supplied from the refrigerant pipe 12 connected to the lower part of the heat exchanger 2 and discharged from the refrigerant pipe 11 connected to the upper part of the heat exchanger 2. By connecting in this way, the vinyl ester can be efficiently cooled and the ethylene absorption efficiency is good. There is no particular limitation on the cooling medium, and alcohol aqueous solutions such as methanol, ethanol, ethylene glycol, glycerin, aqueous solutions of salt or calcium chloride, fluorocarbons, etc. can be used. From the perspective of ease of operation or cost, it is more appropriate to use alcohol aqueous solutions, especially methanol aqueous solutions.

A gas discharge pipe 13 for discharging gas from the heat exchanger 2 is connected to the upper part of the heat exchanger 2. A mist separator (not shown) is connected to the gas discharge pipe 13. Liquid droplets in the discharged gas are removed by the mist separator, and mist-free ethylene can be recovered or released. The mist separator is a device that separates liquid droplets floating in the gas by using external forces such as gravity, centrifugal force, and electrostatic force, or shielding or screening effects. As mist separators, gravity settlers, cyclones, electric dust collectors, scrubbers, bag filters, and packing layers can be cited. Among them, a cyclone is preferred.

There is no particular limitation on the method of bringing vinyl ester into contact with the ethylene-containing gas in the heat exchanger 2. For example, there can be cited a method in which vinyl ester is made to flow down from the upper part of the heat exchanger 2, and the pressurized ethylene-containing gas is supplied to the lower part of the heat exchanger 2, and the two are brought into contact in countercurrent in the heat exchanger 2; or a method in which vinyl ester is made to flow down from the upper part of the heat exchanger 2, and the pressurized ethylene-containing gas is supplied to the upper part of the heat exchanger 2, and the two are brought into contact in parallel flow in the heat exchanger 2. From the viewpoint of efficient ethylene absorption, the former is preferred.

In the apparatus shown in FIG1 , two branch pipes 3 and 4 connect the polymerization tank 1 and the heat exchanger 2. The gas containing ethylene is introduced from the polymerization tank 1 to the lower part of the heat exchanger 2 through the pipe 3, and the vinyl ester after absorbing ethylene is introduced from the lower part of the heat exchanger 2 to the polymerization tank 1 through the pipe 4.

The vinyl ester is supplied to the heat exchanger 2 through the introduction pipe 10. The vinyl ester introduced to the upper portion of the heat exchanger 2 absorbs ethylene while passing through the heat exchanger 2.

The gas containing ethylene is introduced into the heat exchanger 2 through the conduit 3 connected to the lower part of the heat exchanger 2. The conduit 3 on the heat exchanger side is connected to the lower part of the heat exchanger 2, and the vinyl ester introduction pipe 10 is connected to the upper part of the heat exchanger 2. The gas containing ethylene rises in the heat exchanger 2 while being in countercurrent contact with the vinyl ester. As a result, the ethylene in the gas dissolves in the vinyl ester.

The vinyl ester after absorbing ethylene is introduced into the polymerization tank 1 through the conduit 4. During continuous production, ethylene circulates in the polymerization tank 1, the heat exchanger 2, and the conduits 3 and 4. Since part of the ethylene is contained in the vinyl ester and discharged from the reaction liquid outlet pipe 9, it is replenished from the ethylene supply source connected to the polymerization tank 1 through at least one of the conduits 5, 6, and 7.

(Saponification step) The ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl ester copolymer obtained in the polymerization step. At this time, it is preferred to saponify the ethylene-vinyl ester copolymer by alcoholysis or hydrolysis reaction in an organic solvent in the presence of a catalyst. As the catalyst used in the saponification step, there can be mentioned alkaline catalysts such as sodium hydroxide, potassium hydroxide, sodium methoxide, etc.; or acidic catalysts such as sulfuric acid, hydrochloric acid, p-toluenesulfonic acid, etc. There are no particular limitations on the organic solvent used in the saponification step, and examples include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene, etc. These can be used alone or in combination of two or more. Among them, using methanol or a mixed solution of methanol and methyl acetate as a solvent, and carrying out the saponification reaction in the presence of sodium hydroxide as an alkaline catalyst is simple and preferred. The amount of the saponification catalyst used is preferably 0.001 to 0.5 in terms of molar ratio relative to the vinyl ester unit in the ethylene-vinyl ester copolymer. The molar ratio is more preferably 0.002 or more. On the other hand, the molar ratio is more preferably 0.4 or less, and particularly preferably 0.3 or less.

After the saponification step, a pulverization step and a drying step may be performed. Furthermore, the pulverization step may be divided into a preliminary pulverization step and a main pulverization step. After the saponification step, a washing step for removing impurities such as sodium acetate may be performed as needed.

(Compounds with conjugated double bonds) The paper coating of the present invention preferably further contains a compound with a molecular weight of 1000 or less having a conjugated double bond. By using the aforementioned compound, the stability or barrier property of the coating is improved. Although the mechanism is not clear, it is speculated that it is caused by the interaction between the conjugated double bond site and the ethylene unit of the aforementioned ethylene-vinyl alcohol copolymer, and the intermolecular interaction between the aforementioned ethylene-vinyl alcohol copolymer is moderately hindered.

The compound having a molecular weight of 1000 or less having a conjugated double bond in the present invention is a compound having a conjugated double bond between aliphatic double bonds or a compound having a conjugated double bond between an aliphatic double bond and an aromatic ring. From the perspective of the stability or barrier properties of the coating agent, the former is preferred. The molecular weight is 1000 or less, preferably 800 or less, and more preferably 500 or less.

Compounds having conjugated double bonds between aliphatic double bonds are compounds having a structure in which carbon-carbon double bonds and carbon-carbon single bonds are alternately linked, and the number of carbon-carbon double bonds is 2 or more. Specifically, there are conjugated diene compounds having a conjugated structure in which 2 carbon-carbon double bonds and 1 carbon-carbon single bond are alternately linked, conjugated triene compounds having a conjugated structure in which 3 carbon-carbon double bonds and 2 carbon-carbon single bonds are alternately linked (e.g., 2,4,6-octatriene), and conjugated polyene compounds having a conjugated structure in which the number of carbon-carbon double bonds and carbon-carbon single bonds alternately linked is greater than the above. Among them, from the perspective of the stability or barrier properties of the coating agent, the preferred ones are conjugated diene compounds. In the compound with a molecular weight of 1000 or less having conjugated double bonds used in the present invention, the conjugated double bonds can be independent or multiple groups in one molecule, for example, tung oil also contains a compound with three conjugated trienes in the same molecule.

The compound having a molecular weight of 1000 or less and having a conjugated double bond may also have other functional groups in addition to the conjugated double bond. Examples of other functional groups include carboxyl groups and their salts, hydroxyl groups, ester groups, carbonyl groups, ether groups, amino groups, dialkylamino groups, imino groups, amide groups, cyano groups, diazo groups, nitro groups, hydroxyl groups, sulfonyl groups, sulfide groups, thiol groups, sulfonic acid groups and their salts, phosphoric acid groups and their salts, polar groups such as halogen atoms, and non-polar groups such as phenyl groups. From the perspective of the stability or barrier properties of the coating, other functional groups are preferably polar groups, more preferably carboxyl groups and their salts, and hydroxyl groups. Other functional groups may be directly bonded to the carbon atom in the conjugated double bond, or may be bonded to a position remote from the conjugated double bond. The multiple bonds in other functional groups may be at a position that is conjugated to the aforementioned conjugated double bond, for example, 1-phenyl-1,3-butadiene having a phenyl group or sorbic acid having a carboxyl group may also be used as the aforementioned compound having a conjugated double bond. Furthermore, the aforementioned compound having a molecular weight of 1000 or less having a conjugated double bond may also have a non-conjugated double bond or a non-conjugated triple bond.

Specific examples of the aforementioned compound having a molecular weight of 1000 or less having a conjugated double bond include compounds having aliphatic double bonds conjugated to each other such as 2,3-dimethyl-1,3-butadiene, 4-methyl-1,3-pentadiene, 1-phenyl-1,3-butadiene, sorbic acid, myricene, etc., or compounds having aliphatic double bonds conjugated to aromatic rings such as 2,4-diphenyl-4-methyl-1-pentene, α-methylstyrene polymer, 1,3-diphenyl-1-butene, etc.

In the aforementioned paper coating agent, the content of the compound having a molecular weight of 1000 or less and having a conjugated double bond is preferably 0.000001 to 0.01 parts by mass relative to 100 parts by mass of the aforementioned ethylene-vinyl alcohol copolymer. The content is more preferably 0.000002 parts by mass or more, and particularly preferably 0.000003 parts by mass or more. On the other hand, the aforementioned content is more preferably 0.0075 parts by mass or less, particularly preferably 0.005 parts by mass or less, and particularly preferably 0.0025 parts by mass or less.

In the present invention, the method for adding the compound having a molecular weight of 1000 or less and having a conjugated double bond is not particularly limited. For example, there can be cited (1) a method of adding the aforementioned compound to the obtained ethylene-vinyl ester copolymer and then saponifying it, (2) a method of adding the aforementioned compound while saponifying the ethylene-vinyl ester copolymer, (3) a method of spraying a liquid containing the aforementioned compound on the ethylene-vinyl alcohol copolymer, (4) a method of impregnating the ethylene-vinyl alcohol copolymer in a liquid containing the aforementioned compound and then drying it, (5) a method of preparing an aqueous solution containing the ethylene-vinyl alcohol copolymer and the aforementioned compound and then drying it, (6) a method of preparing an aqueous solution containing the ethylene-vinyl alcohol copolymer and the aforementioned compound and using the aqueous solution for various purposes, etc. Among them, from the viewpoint of easy adjustment of the content of the aforementioned compound, the methods (2) and (6) are preferred.

[Paper coating agent] The aforementioned paper coating agent is preferably a solution in which the aforementioned ethylene-vinyl alcohol copolymer has been dissolved, and more preferably an aqueous solution. When the aforementioned paper coating agent contains the ionic polymer described below, the ionic polymer can be dissolved in the solution in which the aforementioned ethylene-vinyl alcohol copolymer has been dissolved, or can be dispersed. The total amount of solid components in the aforementioned solution is usually 50% by mass or less, preferably 40% by mass or less, and more preferably 30% by mass or less.

The aqueous solution in which the ethylene-vinyl alcohol copolymer is dissolved and used as the coating agent of the present invention may also contain alcohols such as methanol, ethylene glycol, glycerin, and water-soluble organic solvents such as cellosol. The content of the organic solvent is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and particularly preferably 10 parts by mass or less relative to 100 parts by mass of water. It is particularly preferred that the aqueous solution does not contain solvents other than water.

The content of the ethylene-vinyl alcohol copolymer in the paper coating agent is preferably 0.1 to 30% by mass. When the content is 0.1% by mass or more, the coating efficiency is more excellent. The content is more preferably 0.5% by mass or more, particularly preferably 2% by mass or more, and particularly preferably 5% by mass or more. On the other hand, when the content is 30% by mass or less, the coating property is more excellent. The content is more preferably 25% by mass or less.

(Ionic polymer) The paper coating of the present invention preferably contains an ionic polymer. Since the paper coating of the present invention contains an ionic polymer, the barrier property of the folded portion formed when the coated paper obtained by using the paper coating has excellent barrier properties. The so-called ionic polymer in the present invention means a polymer compound having a cross-linked structure or a coagulated structure between molecules caused by ions. For example, a polymer compound having an ionic functional group can be cited as having a structure in which at least a part of the ionic functional groups are bonded or interacted by ions, so that the aforementioned polymer compounds have a cross-linked or coagulated structure. The aforementioned ions are not particularly limited, and may be cations or anions, for example, metal ions of the first group of the periodic table such as sodium ions and potassium ions; metal ions of the second group of the periodic table such as magnesium ions; metal ions of the twelfth group of the periodic table such as zinc ions; organic cations such as organic ammonium ions; halide ions such as chloride ions and bromide ions, etc. The aforementioned polymer compound having an ionic functional group is not particularly limited, for example, copolymers of olefins and unsaturated carboxylic acids and/or their derivatives can be cited. As the aforementioned olefins, for example, ethylene, propylene, styrene, etc. can be cited, among which ethylene is preferred. Examples of the unsaturated carboxylic acid include (meth)acrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, isocrotonic acid, liraconic acid, allylsuccinic acid, mesaconic acid, glutaconic acid, nadic acid, methylnadic acid, tetrahydrophthalic acid, methylhexahydrophthalic acid, etc., among which acrylic acid and methacrylic acid are preferred. Examples of the derivative of the unsaturated carboxylic acid include unsaturated carboxylic acid esters, unsaturated carboxylic acid anhydrides, and metal salts of unsaturated carboxylic acids. Specifically, examples of the polymer compound having an ionic functional group include ethylene-(meth)acrylic acid copolymers, ethylene-(meth)acrylic acid-(meth)acrylic acid ester copolymers, and styrene graft polymers of ethylene-(meth)acrylic acid copolymers.

When the paper coating agent of the present invention contains an ionic polymer, the content of the ionic polymer in the paper coating agent is preferably 0.1 mass % or more, more preferably 0.5 mass % or more. If the aforementioned content is above the aforementioned lower limit, the barrier property of the folded portion of the coated paper produced using the paper coating agent when it is folded is excellent. On the other hand, the aforementioned content is preferably 30 mass % or less, more preferably 25 mass % or less, and particularly preferably 20 mass % or less. If the aforementioned content is below the aforementioned upper limit, the barrier property of the flat portion of the coated paper produced using the paper coating agent is excellent.

When the paper coating of the present invention contains an ionic polymer, from the viewpoint of excellent barrier properties of the folded portion of the obtained coated paper, the mass ratio of the ethylene-vinyl alcohol copolymer to the ionic polymer in the paper coating (ethylene-vinyl alcohol copolymer/ionic polymer) is preferably 99/1 or less, more preferably 97/3 or less, particularly preferably 94/6 or less, and particularly preferably 92/8 or less. On the other hand, from the viewpoint of excellent barrier properties of the flat portion of the obtained coated paper, the mass ratio (ethylene-vinyl alcohol copolymer/ionic polymer) is preferably 1/99 or more, more preferably 5/95 or more, particularly preferably 25/75 or more, particularly preferably 50/50 or more, and most preferably 65/35 or more.

The above-mentioned effect of adding the ionic polymer can be achieved even when using an ethylene-vinyl alcohol copolymer whose block characteristic value of the ethylene unit is not within the above-mentioned range. Therefore, a coating agent containing an ethylene-vinyl alcohol copolymer and an ionic polymer whose ethylene unit content is greater than 1 mol% and less than 20 mol% can also be applied to paper applications. Except for not limiting the above-mentioned block characteristic value, suitable aspects of the ethylene-vinyl alcohol copolymer and the ionic polymer contained in the coating agent and other suitable aspects of the coating agent are the same as those of the coating agent containing an ethylene-vinyl alcohol copolymer whose block characteristic value of the ethylene unit is within the specific range. In addition, the following is cited as a suitable implementation aspect of such a coating agent.

The coating agent of the present invention may contain various additives such as glyoxal, urea resin, melamine resin, polyvalent metal salt, water-soluble polyamide resin, etc. water-resistant agents; glycol, glycerin, etc. plasticizers; ammonia, caustic soda, sodium carbonate, phosphoric acid, etc. pH adjusters; defoamers; mold release agents; surfactants; colorants such as pigments, etc., as needed. Furthermore, within the scope that does not hinder the effect of the present invention, the coating agent of the present invention may contain modified PVA other than ethylene-vinyl alcohol copolymer such as unmodified PVA, carboxyl-modified PVA, sulfonic acid-modified PVA, acrylamide-modified PVA, cationic-modified PVA, long-chain alkyl-modified PVA, etc.; casein, raw starch (wheat, corn, rice, potato, sweet potato, cassava, sago), raw starch decomposition products Water-soluble polymers such as dextrin (dextrin, etc.), starch derivatives (oxidized starch, etherified starch, esterified starch, cationized starch, etc.), seaweed polysaccharides (sodium alginate, carrageenan, agar (agarose, agar), fuchsia algae, etc.); synthetic resin emulsions such as styrene-butadiene copolymer emulsions, polyacrylate emulsions, vinyl acetate-ethylene copolymer emulsions, and vinyl acetate-acrylate copolymer emulsions.

The coating agent of the present invention is used for various paper applications excluding adhesives, such as a coating agent for forming a gap filling layer in release paper base paper, a coating agent for forming an oil-resistant layer in oil-resistant paper, a transparent coating agent, a white or colored coating agent containing a pigment, a coating agent for forming an ink receiving layer in inkjet recording materials, a coating agent for forming a protective layer or a thermosensitive coloring layer in thermosensitive recording materials, etc.

[Coated paper] A suitable embodiment of the present invention is a coated paper formed by coating the aforementioned coating agent on paper. As the base paper used for the coated paper, it is possible to use chemical pulp such as broadleaf kraft pulp, conifer kraft pulp, or mechanical pulp such as GP (wood pulp), RGP (refined pulp), TMP (thermomechanical pulp), or synthetic paper made by papermaking. In addition, as the above-mentioned paper, it is also possible to use high-quality paper, medium-quality paper, alkaline paper, glass paper, semi-glass paper, or board paper used for corrugated paper, building materials, white paperboard, white rough paperboard, rough paperboard, etc., white board paper, etc. The basis weight of the front paper can be adjusted according to the application and is not particularly limited, but is usually 10 to 500 g/ ^m2 or less, preferably 40 to 200 g/ ^m2 . In addition, the paper used for the coated paper may contain organic or inorganic pigments, or paper strength enhancers, sizing agents, yield enhancers and other papermaking auxiliary chemicals. In addition, the paper used for the coated paper may be subjected to various surface treatments.

The coating amount of the aforementioned coating agent can be arbitrarily selected according to the properties and shape of the paper to be coated, but it is usually preferably about 0.1 to 30 g/ ^m2 in terms of solid content. The aforementioned coating agent can be applied to the surface of the paper, or it can be impregnated into the inside. Moreover, in the former case, the aforementioned coating agent can be applied to one side of the paper, or it can be applied to both sides. Since the coating agent of the present invention is easy to form a film, even if the coating amount is small, a coating layer containing the aforementioned ethylene-vinyl alcohol copolymer can be formed near the surface of the paper to enhance the barrier properties. From the viewpoint of making better use of such characteristics, it is better to apply the aforementioned coating agent to the surface of the paper.

As a method of applying the coating agent obtained by dissolving the aforementioned ethylene-vinyl alcohol copolymer in a solution onto paper, there can be cited a transfer method using a sym-sizer, a horizontal roller coater, or the like, and an impregnation method using a glue press, or the like. From the viewpoint of being easier to form a coating layer, the transfer method is preferred. On the other hand, since the coating agent of the present invention is easy to form a film, even when an impregnation method is used, the aforementioned coating agent is inhibited from penetrating into the interior of the paper, and a coating layer can be efficiently formed near the surface. Therefore, the coating amount is reduced, and drying is also easier, thereby reducing costs. The temperature of the aforementioned coating agent during application is generally room temperature to 100°C.

The drying of the paper coated with the solution of the coating agent can be carried out by well-known methods, such as hot air, infrared, heating cylinder or a combination of these methods. The drying temperature is usually room temperature to 120°C. The barrier property can be further improved by moisturizing and calendering the dried coated paper. As the calendering treatment conditions, the roll temperature is usually room temperature to 100°C, and the roll line pressure is 20 to 300 kg/cm.

The coated paper may have a layer other than the coating layer containing the ethylene-vinyl alcohol copolymer, such as a release layer described later.

The coated paper obtained by coating the aforementioned coating agent on paper can also be used as special paper such as release paper, oil-resistant paper, thermal paper, inkjet paper, pressure-sensitive paper, air-barrier paper, and other barrier papers, among which it is more suitable for use as release paper and oil-resistant paper.

[Release paper base] The release paper base formed by the aforementioned coated paper is a more suitable embodiment of the present invention. When a release layer is formed on this release paper base, the aforementioned coating agent serves as a filler. That is, the release paper base formed by coating the aforementioned coating agent on paper is a paper base having a filler layer (barrier layer) formed on the paper. The filler layer formed using the coating agent of the present invention has excellent barrier properties and water resistance, so it can inhibit the later-described release agent from penetrating into the paper. Moreover, even when a water-dispersible varnish or the like is used, the barrier properties of the aforementioned filler layer are maintained. The aforementioned filler layer is formed on at least one side of the aforementioned paper. The coating amount of the coating agent can be arbitrarily selected according to the properties and shape of the paper to be coated, but it is preferably about 0.3 to 3 g/ ^m2 per single side of the paper.

From the perspective of further improving the barrier properties, the air permeability resistance of the above-mentioned release paper base paper measured by using a Wangyan type smoothness air permeability tester according to JIS P8117 (2009) is preferably 20,000 seconds or more, more preferably 30,000 seconds or more, and even more preferably 37,000 seconds or more.

[Release paper] A release paper having a release layer formed on the release base paper is a suitable embodiment of the release base paper. The release layer is formed on the interstitial layer. The release paper obtained can be applied to adhesive labels, adhesive tapes, industrial adhesive papers, release papers, etc. As the release layer, a polysilicone resin is preferably used. As a release agent for forming such a release layer, solvent-based polysilicone and non-solvent-based (emulsion-based, oligomer-based) polysilicone can be cited. As the solvent containing the stripping agent, there can be mentioned an organic solvent such as toluene.

In addition to the above-mentioned ingredients, the release layer of the release paper of the present invention may also contain pigments used in papermaking, fluorescent brighteners, substances to be stained by fluorescent brighteners, defoaming agents, mold release agents, coloring agents, water retaining agents and other drugs.

The coating of the aforementioned release agent can be carried out using common paper coating equipment. For example, the coating agent can be applied to the paper in one or more layers by using an on-machine coating machine or off-machine coating machine equipped with a coating device such as a doctor blade coating machine, an air knife coating machine, a transfer roller coating machine, a rod metal glue press coating machine, a curtain coating machine, a wire rod coating machine, etc. In addition, as a drying method after coating, various heating drying methods such as a hot rotary drum, hot air heating, gas stove heating, infrared heater heating, etc. can be appropriately adopted. The coating amount of the stripping agent is usually 0.1 to 2 g/m ² in terms of solid content.

In addition, as the water-dispersible varnish used for post-processing, there can be cited conjugated diene latexes such as styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, styrene-methyl methacrylate-butadiene copolymer latex, etc.; acrylic latexes such as polymer latex or copolymer latex of acrylate and/or methacrylate; vinyl latexes such as ethylene-vinyl acetate polymer latex, etc., and one or more of them can be appropriately selected and used.

[Oil-resistant paper] Oil-resistant paper formed by the aforementioned coated paper is also a more suitable embodiment of the present invention. In the aforementioned oil-resistant paper, the aforementioned coating agent is coated on at least one side of the aforementioned paper to form a coating layer. The oil-resistant paper with the coating layer formed in this way has both high oil resistance and water resistance. As a coating method of the aforementioned coating agent, the above method is adopted in the method of forming the gap filling layer of the aforementioned release paper base paper. The coating amount of the aforementioned coating agent is usually 0.1 to 20 g/ ^m2 in terms of solid content. [Example]

Next, examples are given to more specifically illustrate the present invention, but the present invention is not limited to these examples. Furthermore, in the examples and comparative examples, "%" and "parts" represent "mass %" and "mass parts" respectively unless otherwise specified.

[Viscosity average polymerization degree and saponification degree of ethylene-vinyl alcohol copolymer] The viscosity average polymerization degree and saponification degree of ethylene-vinyl alcohol copolymer are calculated according to the method described in JIS K6726 (1994).

[Block characteristic value of ethylene unit in ethylene-vinyl alcohol copolymer] After saponification of ethylene-vinyl alcohol copolymer to a saponification degree of 99.9 mol% or more, the copolymer was fully washed with methanol and then dried under reduced pressure at 90°C for 2 days. The copolymer was dissolved in DMSO-d ₆ and measured at 80°C using 600MHz ¹³ C-NMR. From the obtained spectrum, the molar fraction of vinyl alcohol-ethylene 2-unit chain (AE), the molar fraction of vinyl alcohol unit (A), and the molar fraction of ethylene unit (E) were attributed and calculated by the method described in T. Moritani and H. Iwasaki, 11, 1251-1259, Macromolecules (1978), and the block characteristic value (η) of ethylene unit was calculated by the following formula. η=(AE)/{2×(A)×(E)}

[Viscosity stability of paper coating agent] The ratio (η 1 /η 0 ) of the initial viscosity (η ₀ ) of the aqueous solution of the coating agent at 30°C to the viscosity (η ₁ ) of the aqueous solution placed in a 300 ml glass beaker at 30°C for 1 day was determined _and evaluated using the following criteria. The measurement was performed at 30°C using a B-type viscometer (rotation speed 12 rpm) in _accordance with the rotational viscometer method of JIS K6726 (1994). A: η ₁ /η ₀ is 1 or more and less than 5, and gelation and phase separation of the aqueous solution do not occur. B: η ₁ /η ₀ is 5 or more and less than 10, and gelation and phase separation of the aqueous solution do not occur. C: η ₁ /η ₀ is 10 or more, or the aqueous solution undergoes gelation or phase separation.

[Evaluation of coated paper] (1) Air resistance According to JIS P8117 (2009), the air resistance of coated paper is measured using a Wangyan-type smoothness air permeability tester. The air resistance value indicates the time it takes for 100 mL of air to pass through a certain area. Therefore, the larger the air resistance value, the more difficult it is for air to pass through, indicating a high gap filling property.

(2) Oil-based ink printout Use an oil-based pen to print on one side of the coated paper, and visually observe the ink printout on the non-printed side. Evaluate using the following criteria. A: No printout B: Partial printout C: Full printout

(3) Water-resistant surface strength After dropping about 0.1 ml of ion-exchanged water at 20°C on the surface of the coating paper, rub it with your fingertips and observe the dissolution state of the coating agent. Evaluate it according to the following criteria. A: No mucus feeling B: Mucus feeling, or part of the coating agent has been emulsified C: The coating agent is completely emulsified or dissolved

(4) Oil resistance For the coated paper prepared for oil resistance measurement, the oil resistance of the flat part and the oil resistance of the bent part are measured according to the following method. (Oil resistance of the flat part) The oil resistance of the coated surface (flat part) is measured according to TAPPI No.T559cm-02. The measurement is performed by visual inspection. In addition, the oil resistance (KIT value) of commercially available oil-resistant paper using fluororesin is usually above level 5, and the oil resistance with no problem in general use is above level 5. Therefore, the oil resistance of the coated paper is preferably above level 5, and in applications requiring higher oil resistance, it is preferably above level 7, and more preferably above level 10. (Oil resistance of folded portion) Fold the coated paper in half with the coated surface as the outside, press down on the folded portion to completely crease it at a width of 1.0 mm, a depth of 0.7 mm, and a pressure of 2.5 kgf/cm ² sec, then unfold the coated paper and measure the oil resistance of the folded portion in accordance with TAPPI No. T559cm-02. The measurement is performed by visual inspection. As for the folded portion, since the oil resistance without any problem is also above level 5, the oil resistance of this portion is preferably above level 5. In applications requiring higher oil resistance, it is preferably above level 7, and more preferably above level 10.

FIG1 shows a schematic diagram of the polymerization apparatus used. In a substantially cylindrical polymerization tank 1 [capacity: 7 kl, tank inner diameter D: 1.8 m] equipped with a Maxblend blade [manufactured by Kobelco Environmental Solutions Co., Ltd., agitator blade diameter (diameter) d: 1.1 m, blade (paddle) width b: 1.5 m] as agitator blade 8, ethylene was introduced from conduit 5 so that the ethylene pressure in the tank became 0.23 MPa, and a 1 mass % methanol solution of 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile) as a polymerization initiator was introduced from conduit 6 at a rate of 3 L/hr. Furthermore, a liquid containing vinyl acetate (vinyl acetate: 777 L/hr, methanol: 170 L/hr) was introduced into the polymerization tank 1 through the introduction pipe 10 and the heat exchanger 2. In addition, a gas containing ethylene is introduced from the polymerization tank 1 to the heat exchanger 2 through the conduit 3. A liquid containing vinyl acetate flows down along the surface of the tube and absorbs ethylene, and is injected into the polymerization tank 1 through the conduit 4, mixed with the reaction liquid, and provided for continuous polymerization of ethylene. The polymerization liquid is continuously taken out from the conduit 9 in such a way that the liquid level in the polymerization tank 1 becomes constant. The polymerization rate of vinyl acetate at the outlet of the polymerization tank 1 is adjusted to be 30%. In addition, the stirring power Pv per unit volume is 2.2 kW/ ^m3 , and the Fr is adjusted to be 0.13. The entire blade is immersed in the reaction liquid, and the reaction liquid is stirred in a state where the liquid level is close to the upper end of the blade. The residence time of the reaction liquid in the polymerization tank is 5 hours. The temperature at the outlet of the polymerization tank was 60° C. By introducing methanol vapor into the continuously withdrawn polymerization solution, unreacted vinyl acetate monomer was removed to obtain a methanol solution of ethylene-vinyl acetate copolymer (concentration 32 mass %).

To the methanol solution (concentration 32 mass %) of the ethylene-vinyl acetate copolymer obtained in the above polymerization step, a methanol solution (concentration 4 mass %) of sodium hydroxide as a saponification catalyst was added, wherein the molar ratio of sodium hydroxide to the vinyl acetate unit in the above ethylene-vinyl acetate copolymer was 0.012. Furthermore, 0.00009 mass parts of a methanol solution of sorbic acid (concentration 10 mass %) was added based on the solid content per 100 mass parts of the above ethylene-vinyl acetate copolymer, and the resulting mixture was mixed with a static mixer, placed on a belt, and maintained at 40° C. for 18 minutes to perform a saponification reaction. Then, the above mixture was pulverized and dried to obtain an ethylene-vinyl alcohol copolymer (A-1) (hereinafter referred to as copolymer (A-1)). The obtained copolymer (A-1) had an ethylene unit content of 2 mol %, a viscosity average polymerization degree of 1700, a saponification degree of 98.5 mol %, a block characteristic value of ethylene units of 0.95, and a sorbic acid content of 0.00018 parts by mass relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer.

(Manufacturing of copolymers (A-2), (A-3), (A-5), (A-6) and PVA-7) In addition to changing the amount of ethylene, vinyl acetate, methanol and initiator fed during polymerization, the polymerization rate, the type of agitator blade (A-6: anchor blade, agitator blade diameter (diameter) d: 1.7m, blade (paddle) width b: 0.85m, due to the small blade (paddle) width b, it is not equivalent to a wide paddle Except for the addition of the impeller, stirring power Pv, Fr, concentration of the ethylene-vinyl ester copolymer solution during saponification, molar ratio of sodium hydroxide, and the type and amount of the compound containing a conjugated double bond, ethylene-vinyl alcohol copolymers (copolymers (A-2), (A-3), (A-5), (A-6)) and PVA (PVA-7) were prepared by the same method as the copolymer (A-1). Table 1 summarizes the polymerization conditions and saponification conditions during the preparation, the polymerization degree, saponification degree, ethylene unit and block characteristic values of the obtained polymers, and the type and content of the compound containing a conjugated double bond.

(Production of Copolymer (A-4)) In a polymerization tank 1 [capacity: 7 kl, tank inner diameter D: 1.8 m] equipped with a two-stage inclined paddle [paddle diameter (diameter) d: 1.5 m, paddle width b: 0.88 m] as a stirring blade 8, ethylene was introduced from a conduit 5 so that the ethylene pressure in the tank became 0.61 MPa, and a 1 mass % methanol solution of 2,2'-azobis-(4-methoxy-2,4-dimethylvaleronitrile) as a polymerization initiator was introduced from a conduit 6 at a rate of 9 L/hr. Furthermore, a liquid containing vinyl acetate (vinyl acetate: 751 L/hr, methanol: 190 L/hr) was introduced into the polymerization tank 1 from an introduction pipe 7. The polymerization liquid is continuously taken out from the conduit 9 in such a manner that the liquid level in the polymerization tank 1 becomes constant. The polymerization rate at the outlet of the polymerization tank 1 is adjusted to be 43%. In addition, the stirring power Pv is 2 kW/m ³ and the Fr is adjusted to be 0.18. The residence time of the reaction liquid in the polymerization tank is 5 hours. The temperature at the outlet of the polymerization tank is 60°C. By introducing methanol vapor into the continuously taken out polymerization liquid, unreacted vinyl acetate monomers are removed to obtain a methanol solution (concentration 40 mass %) of ethylene-vinyl acetate copolymer (A-4). Except for changing the concentration of the ethylene-vinyl ester copolymer solution and the molar ratio of sodium hydroxide, the saponification step is carried out in the same way as the copolymer (A-1) to produce an ethylene-vinyl alcohol copolymer (A-4). Table 1 summarizes the polymerization and saponification conditions during production, the degree of polymerization, saponification degree, vinyl unit and block characteristics of the obtained polymer, and the type and content of the compound containing conjugated double bonds.

[Table 1] Polymerization conditions Saponification conditions Ethylene-vinyl alcohol copolymer Ethylene Vinyl acetate Methanol Initiator Polymerization rate Stirring Wing Pv Fr Supply of vinyl acetate PVAc concentration NaOH Ethylene unit (mol%) Degree of Polymerization Saponification degree (mole %) Block characteristic value Compounds containing conjugated double bonds MPa L/hr L/hr L/hr % - kW/m ³ - - Quality% Morelby Type ¹⁾ Content2 ⁾ (weight) A-1 0.23 777 170 3 30 Maxblend Wing 2.2 0.13 Heat exchanger 32 0.012 2 1700 98.5 0.95 S 1.8×10 ^-4 A-2 0.47 820 128 2.5 28 Maxblend Wing 3 0.11 Heat exchanger 30 0.012 4 1700 98.5 0.97 S 1.8×10 ^-4 A-3 0.69 682 185 82.6 70 Maxblend Wing 1.9 0.1 Heat exchanger 45 0.015 10 400 98 0.98 - - A-4 0.61 751 190 9 43 2-stage tilting propeller blades 2 0.18 direct 40 0.02 6 1000 99.2 0.85 S 1.8×10 ^-4 A-5 0.1 745 2 202.7 78 Maxblend Wing 6.9 0.21 Heat exchanger 45 0.008 2 500 88 1.01 S 1.8×10 ^-4 A-6 ³⁾ 1.77 735 174 41 50 Anchor Wing 1.8 0.17 Heat exchanger 40 0.03 twenty two - - 0.99 - - PVA-7 0 700 280 2.5 35 Maxblend Wing 2.1 0.14 Heat exchanger 30 0.01 0 1700 98.5 - DPMP 40× ^10-4 1) SA: sorbic acid, DPMP: 2,4-diphenyl-4-methyl-1-pentene 2) The content of the compound having conjugated double bonds relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer. 3) The obtained ethylene-vinyl alcohol copolymer is insoluble in water.

[Example 1] (Preparation of a coating agent for paper) The obtained ethylene-vinyl alcohol copolymer (A-1) powder (10 parts) was added to stirred water (90 parts, 20°C), and heated to 95°C to obtain a coating agent (aqueous solution) in which the ethylene-vinyl alcohol copolymer (A-1) was dissolved. The viscosity stability of the obtained coating agent was evaluated according to the above method. The results are shown in Table 2.

(Preparation of coated paper for measuring air permeability resistance, oil ink penetration, and water-resistant surface strength) The obtained coating agent was applied to PPC (plain paper copier) paper (premium paper) with a basis weight of 70g/ ^m2 and an air permeability resistance of 20sec using a test 2-roll glue press (manufactured by Kumagai Riki Industry Co., Ltd.) at 50°C and 100m/min, and then dried at 100°C for 5 minutes to obtain coated paper. The coating amount of the above-mentioned coating agent converted to solid content was 0.8g/ ^m2 (total amount on both sides). The obtained coated paper was humidified at 20°C and 65%RH for 72 hours, and the physical properties of the coated paper were evaluated. The results are shown in Table 2.

(Preparation of coated paper for oil resistance measurement) Coated paper was obtained in the same manner as above except that the coating amount calculated as the solid content of the coating agent was changed to 3.5 g/m ² (total amount on both sides). The obtained coated paper was humidified at 20°C and 65% RH for 72 hours, and the physical properties of the coated paper were evaluated. The results are shown in Table 2.

[Examples 2, 3 and Comparative Examples 1 to 4] Except that the ethylene-vinyl alcohol copolymer (A-1) was replaced with the ethylene-vinyl alcohol copolymers (A-2) to (A-6) or PVA-7 shown in Table 2, a coating agent and a coating paper were prepared in the same manner as in Example 1, and the properties of the coating agent and the coating paper were evaluated. The results are shown in Table 2. Moreover, the copolymer (A-6) is insoluble in water and an aqueous solution cannot be obtained.

[Examples 4 to 7] Powder (10 parts) of ethylene-vinyl alcohol copolymer (A-2) was added to stirred water (90 parts, 20°C), and heated to 95°C to obtain an aqueous solution in which ethylene-vinyl alcohol copolymer (A-2) was dissolved. The aqueous solution, an ionic polymer (Chemiperal (registered trademark) S-100 manufactured by Mitsui Chemicals, Inc., a sodium salt aqueous dispersion of ethylene-acrylic acid copolymer) and water as needed were mixed to obtain a coating agent in which the ionic polymer was dispersed in the aqueous solution in which copolymer (A-2) was dissolved. At this time, the addition amounts of the aqueous solution, ionic polymer and water were adjusted so that the composition of the coating agent was as shown in Table 2. The coating agent obtained was evaluated in the same manner as in Example 1. In addition, except for using the obtained coating agent, the same method as in Example 1 was followed to prepare a coated paper and evaluate its physical properties. Table 2 shows the results.

[Comparative Example 5] Except that ethylene-vinyl alcohol copolymer (A-1) was replaced with copolymer (A-4) and 5 parts by weight of carboxymethyl cellulose (CMC) was added to 100 parts by weight of copolymer (A-4), a coated paper was prepared in the same manner as in Example 1 and the physical properties of the coated paper were evaluated. The results are shown in Table 2.

[Table 2] Spray agent Reviews Ethylene-vinyl alcohol copolymer Ionic polymer water Compounds containing conjugated double bonds Coatings Coating paper Type Ethylene unit (mol%) Degree of Polymerization Saponification degree (mole %) Block characteristic value Content (weight) Content (weight) Content (weight) Type ¹⁾ Content2 ⁾ (weight) Viscosity stability Air permeability resistance (sec) Ink penetration Water resistant surface strength Oil resistance Plane Bend Embodiment 1 A-1 2 1700 98.5 0.95 10 - 90 S 1.8×10 ^-4 A 45000 A A 12 3 Embodiment 2 A-2 4 1700 98.5 0.97 10 - 90 S 1.8×10 ^-4 A 50000 A A 12 3 Embodiment 3 A-3 10 400 98 0.98 10 - 90 - - B 35000 A A 10 4 Embodiment 4 A-2 4 1700 98.5 0.97 9 1 90 S 1.8×10 ^-4 A 45000 A A 12 10 Embodiment 5 A-2 4 1700 98.5 0.97 7 3 90 S 1.8×10 ^-4 A 35000 A A 11 10 Embodiment 6 A-2 4 1700 98.5 0.97 3 7 90 S 1.8×10 ^-4 A 25000 A B 7 7 Embodiment 7 A-2 4 1700 98.5 0.97 1 9 90 S 1.8×10 ^-4 A 20000 B B 5 5 Comparison Example 1 A-4 6 1000 99.2 0.85 10 - 90 S 1.8×10 ^-4 B 6000 C A 5 3 Comparison Example 2 A-5 2 500 88 1.01 10 - 90 S 1.8×10 ^-4 A 10000 B C 5 3 Comparative Example 3 ³⁾ A-6 twenty two - - 0.99 - - - - - Comparison Example 4 PVA-7 0 1700 98.5 - 10 - 90 DPMP 40× ^10-4 C 3000 C B 4 2 Comparative Example 5 ⁴⁾ A-4 6 1000 99.2 0.85 10 - 90 S 1.8×10 ^-4 C 12000 B A 3 3 1) DPMP: 2,4-diphenyl-4-methyl-1-pentene, SA: sorbic acid 2) The content of the compound having a conjugated double bond relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer. 3) The obtained ethylene-vinyl alcohol copolymer is insoluble in water. 4) 5 parts by mass of carboxymethyl cellulose is added relative to 100 parts by mass of the copolymer (A-4).

1: Polymerization tank 2: Heat exchanger 3~7: Conduit 8: Mixer 9: Reaction liquid outlet pipe 10: Ethylene ester inlet pipe 11,12: Refrigerant pipe 13: Gas exhaust pipe 21: Maxblend wing 22: Super-Mix MR203 23: Super-Mix MR205 24: Fullzone wing

FIG1 is a schematic diagram of a polymerization device used in an embodiment. FIG2 is a schematic diagram of an example of a wide-blade paddle used in the present invention.

Claims (9)

A coating agent for paper, comprising an ethylene-vinyl alcohol copolymer having an ethylene unit content of 1 mol% or more and less than 20 mol%, and a block character of the ethylene unit of 0.90-0.99, wherein the block character represents the numerical value of the distribution of the ethylene unit and the vinyl alcohol unit generated by the saponification of the vinyl ester unit, and the block character is determined by ¹³ C-NMR as follows: first, the ethylene-vinyl alcohol copolymer is saponified to a saponification degree of 99.9 mol% or more, and then fully washed with methanol and dried under reduced pressure at 90°C for 2 days; the completely saponified ethylene-vinyl alcohol copolymer is dissolved in DMSO-d ₆ , and the sample is measured at 80°C using 500 MHz ¹³ C-NMR; from the obtained spectrum, the spectrum is analyzed using the method of T. Moritani and The molar fraction of vinyl alcohol-ethylene 2-unit chain (AE), the molar fraction of vinyl alcohol unit (A), and the molar fraction of ethylene unit (E) were calculated according to the method described in H.Iwasaki, 11, 1251-1259, Macromolecules (1978). The block characteristic value (η) of ethylene unit was calculated by the following formula: η=(AE)/{2×(A)×(E)}. The paper coating agent of claim 1 contains 0.000001 to 0.01 parts by mass of a compound with a molecular weight of less than 1000 and having a conjugated double bond relative to 100 parts by mass of the ethylene-vinyl alcohol copolymer. For example, the paper coating agent of claim 1 or 2, wherein the saponification degree of the ethylene-vinyl alcohol copolymer is 80-99.7 mol %. For example, the paper coating agent of claim 1 or 2, wherein the viscosity average polymerization degree of the ethylene-vinyl alcohol copolymer is 300-5000. The paper coating agent of claim 1 or 2 further contains an ionic polymer. A coated paper, which is a paper coated with a coating agent as described in any one of claims 1 to 5. For example, the coated paper in claim 6 is the peeling paper base paper. The coating paper in claim 6 is oil-resistant paper. A method for manufacturing coated paper, which comprises applying a coating agent as described in any one of claims 1 to 5 onto paper.